Current display adapters include the capability to provide multiple port access. This means that the single display adapter is actually accessible through two separately addressable ports. This enables applications programs to reference either one port or the other port in accessing the display device.
Prior art in this area of technology includes "Virtual Graphics" by Voorhies, Kirk and Lathrop, published in Computer Graphics, Vol. 22, No. 4, August, 1988. This paper addresses multiple process workstations that include a single task oriented graphics display adapter. This paper addresses the problem of switching display adapter contexts rapidly. This is accomplished by the use of a coprocessor exception based detection of graphic ownership violations (a graphics process attempting to access a device when it does not have access to the device, the efficient swapping of drawing context in hardware, exception based command flow control, the clipping of drawings to window boundaries and the switching of pixel formats and lookup tables for pixels. This reference teaches that additional hardware is a partial solution to the problem of quickly changing display contexts.
The article "Hardware Acceleration for Windows System" by Rhoden and Wilcox, published in Computer Graphics, Vol. 23, No. 3, July, 1989, illustrates a hardware implementation to provide multiple windowing capabilities.
IBM Technical Disclosure Bulletin, Vol. 30, No. 1, June, 1987, entitled "Virtual Machine Interface/Virtual Resource Manager", discloses a context switching mechanism for a virtual machine. In this reference, the complete context for the central processing unit is changed.
IBM Technical Disclosure Bulletin, Vol. 28, No. 8, January, 1986, entitled "Screen-Sharing Ring for Enhanced Multiple Application Display", discloses a technique for laying out display windows that are displayed in dedicated rectangular subareas.
IBM Technical Disclosure Bulletin, Vol. 25, No. 8, January, 1983, entitled "Asynchronous Data Transfer Buffer for NP Systems", discloses a multiprocessing communications system where the processors communicate to each other in order to avoid contention when accessing a commonly shared memory.
IBM Technical Disclosure Bulletin, Vol. 28, No. 12, May, 1986, entitled "Hardware Display Windowing System", discloses a hardware windowing system for use with a display that is shared by multiple processors.
IBM Technical Disclosure Bulletin, Vol. 27, No. 5, October, 1984, entitled "Multiprocessor System to Improve Context Switching", discloses a processing system that reduces context switching by specifying that only one processor is active at a time.
IBM Technical Disclosure Bulletin, Vol. 24, No. 1, November, 1981, entitled "Multi-Tasking Using Co-Equal Multiprocessors Having Memory-Lock Facilities", discloses a locking scheme for a multiprocessing system using a commonly shared memory.